The present invention relates to a thrust mechanism for mill roll bearings and more particularly to a thrust bearing clamp assembly which can be quickly installed on and removed from mill rolls, work rolls in particular, and which affords quick, reliable thrust adjustment.
During the operation of a rolling mill such as a sheet or strip mill, the mill rolls rotate at high speed to process metal feedstock into a strip or similar configuration. The work rolls of a typical mill may rotate at a speed as high as 500 rpm, for example. Each of the rolls of such a mill is supported in bearing assemblies that are housed in bearing chocks or roll boxes, and which desirably include all of the necessary components for the lubrication, sealing, thrust take-up, and positioning of the respective bearing assemblies. It is highly desirable to provide a quick and convenient manner of positioning, seating, and locking the bearing assemblies on the mill rolls, and particularly on the work rolls of the rolling mill, for the reasons set forth below.
In known rolling mills, particularly cold mills, the terminal speed of the strip or other configuration being rolled may approach 6000 feet per minute. In such mills, the rolling forces may exceed one million pounds. At typically encountered speeds and rolling forces, the mill rolls, and particularly the work rolls, are subject to such enormous wearing forces that in many applications the useful life of the roll surface may be limited to about 4 to 8 hours of mill operation. When this limit is reached, regrinding of the work rolls is required. Thus, on a three shift basis, the work rolls of a mill may be changed as often as 180 times per month per mill stand.
Known procedures for changing work rolls have consumed inordinate amounts of time and labor in withdrawing the worn rolls from each mill stand and replacing them with a set of newly surfaced rolls. Roll changing operations thus cause considerable down time of the rolling mill and attendant loss of production. Additional operating personnel, who are not otherwise necessary for the actual operation of the rolling mill, are also required.
A large proportion of the time involved in roll changing operations typically is occupied in dechocking or stripping the roll bearing assemblies from the worn rolls and installing the bearing assemblies on the replacement rolls. As is evident from the foregoing, mill roll dechocking and rechocking are often repeated operations during normal use of the rolling mill. When assemblying the roll bearings on the mill roll necks, it is necessary to provide convenient means for locating the bearing on the roll neck and for taking up any slack, followed by locking of the bearing and the bearing chock in place. To strip the bearing assemblies from the roll necks, the assembly procedure is of course reversed.
Not only have prior art roll bearing assemblies been difficult and incovenient to assemble and disassemble on the roll necks, they have also been difficult to adjust and to lock in place to maintain the adjustment. The thrust on the roll bearings must be properly adjusted in order to ensure proper roll support during operation. If there is longitudinal clearance in the bearing assembly, the roll will be free to shift longitudinally. This can cause a pumping action of lubricant in the bearings and may permit dirt and other impurities to enter the bearing and thereby cause excess wear and possibly premature bearing failure. By the same token, however, the bearings must not be rigidly clamped in place as there are elements of the bearing assembly which will fail prematurely if not free to move. For example, the inner race of a tapered roller bearing, like those which commonly support a rotary roll in a rolling mill, must be free to rotate slowly in response to circumferentially directed force inputs that result from the rotary motion of the roll in order that the weight of the roll will not continuously be supported by only a small portion of the bearing race located under the roll. Accordingly, it will be seen that adjustment of bearing thrust is a critical aspect of roll bearing removal and replacement as the bearings can be neither too loosely nor too tightly retained on the roll neck.
Not only have prior bearing thrust assemblies been inconvenient to assemble and disassemble, and difficult to adjust, they also have presented difficulties in maintaining the desired adjustment, once achieved. Often, prior thrust assemblies have utilized circumferential friction clamp means engaging the roll neck to maintain the desired adjustment. Such a clamping mechanism is not sufficiently positive to ensure maintenance of a specified adjustment and often may loosen or move due to vibration. Such movement generally would be unknown to the mill operators and could result in rapid wear of the bearings to the point of catastrophic failure.
Still another shortcoming of the prior bearing thrust assemblies has been the rough or course nature of the bearing thrust adjustment process, owing to the use of high friction mechanisms such as frictionally engaged ramps or the like on relatively rotatable rings encompassing the roll neck. Manual adjustment of such ramp mechanisms requires an operator to develop a rather sensitive feel for the point of proper thrust adjustment. The inherent difficulty in achieving this end has been increased by the high friction force between confronting ramp elements in prior bearing thrust assemblies. With such friction force to be overcome, the feel of proper bearing thrust adjustment is largly obscured and the likelihood that proper adjustment will be achieved is correspondingly reduced.
Yet another shortcoming of prior bearing thrust assemblies for rolling mills has been the difficulty encountered in retrofitting a universal bearing thrust assembly to a wide variety of different mill roll neck designs and specifications.
For the above and numerous other reasons, practitioners of the art have continually sought to improve existing mill bearing thrust assemblies.